The present invention generally relates to a dew-point adjusting method and apparatus which is effective for use in an apparatus for drying photographic film, printing paper, etc., in the manufacture of photosensitive materials. More particularly, the invention relates to a dew point adjusting method and apparatus using dry dehumidifiers, in which drying air to be sent to a drying apparatus is adjusted so as to have a fixed dew point.
Adjustment apparatuses for adjusting drying air to be sent to a drying apparatus so as to have a fixed dew point can be classified into two types, one using wet dehumidifiers and the other using dry dehumidifiers. In a wet-type adjustment apparatus using wet dehumidifiers, it is possible to relatively easily generate drying air having a fixed dew point from the start of operation of the drying apparatus until the drying apparatus has reached steady-state operation in which the dew point of the air therein is constant using a method in which water is sprayed into the air. This type of apparatus is similar to an air cleaning apparatus.
On the other hand, in the case of a dry-type adjustment apparatus using dry dehumidifiers, the dry-bulb temperature and the dew point of the air in the drying apparatus sucked into the dry dehumidifiers rapidly change at the beginning of operation of the drying apparatus and cannot be stabilized before the drying apparatus has reached its steady operating state. In such an apparatus, therefore, it has been difficult to adjust the air in response to changes in the dry-bulb temperature and the dew point of the air so as to have a fixed dew point. Thus, it is difficult to supply properly adjusted air to the drying apparatus.
In order to solve this problem, a method has been used in which, as shown in FIG. 3, a humidifier 36 is provided in a duct 2 of a dehumidifier 35 for sucking circulating air from a apparatus 1. The humidifier 36 sprays water or steam so as to stabilize the dew point of the circulating air from the drying apparatus 1 before the dew point of the circulating air has stabilized. The air with its dew point so adjusted is supplied to the dehumidifier 35. The humidifier 36 is stopped after the dew point of the circulating air has become stable. Thereafter, the adjustment of the dew point is performed using only the dehumidifier 35.
In the method in which a humidifier for circulating air is provided at a suction side of a dehumidifier and in which the humidifier is stopped through predetermined control, it is difficult to accurately carry out the control operation. Accordingly, it has been almost impossible to stabilize the dew point of the circulating air, particularly when a dry dehumidifier having a slow control response is used.
In the coating and drying of a photosensitive material, changes in drying rate occur due to variations in the dew point of the drying air. These changes in drying rate are a problem from the viewpoint of quality and yield, especially in the manufacture of photosensitive materials.
Therefore, it is desired to provide drying air having a fixed dew point from the start of operation of the drying apparatus until the drying apparatus has reached its steady operating state.